The present invention relates to providing precision coatings to substrates and more particularly to the coating of substrates with modular coating apparatus adapted to provide various desired results including no edge beading, no edge coating, reduced material loss, reduced cleaning solvent usage, and increased processing throughput.
Providing coatings of a desired thickness and uniformity on a substrate has been a necessity in many industries, most notably in the processing of silicon wafers to produce integrated circuits (xe2x80x9cchipsxe2x80x9d). For example, in the production of chips, a wafer may be coated with photoresist in order to develop a mask for controlling the introduction of dopants into or onto the wafer. However, due to the typically very large scale integration of electrical components (often in the hundreds of thousands and even in the millions) integrated into a single chip, many of which are produced from a single wafer, tolerances with respect to providing these coatings are very narrow. Likewise, as particular areas to be defined by such coatings may be very small, such as on an order of magnitude equivalent with the wavelength of light, the cleanliness and purity requirements of such coatings and coating processes are high. Moreover, the chemicals used are often very costly and/or very volatile and, therefore, it is generally desired that their use, dispensation, and handling be strictly controlled so as to not unnecessarily waste such chemicals and/or cause additional costs in their clean-up and subsequent handling in addition to environmental concerns.
The current state of the art in coating wafers is to provide a relatively large amount of coating material at or near the center of a wafer to be coated and then to rapidly spin the wafer for a precisely controlled time and at a precisely controlled speed. Such spinning, although generally providing a coating of the substrate wafer having an acceptable thickness and uniformity, results in a great deal of wasted coating material as a relatively large amount of such material, in proportion to that remaining as a coating of the substrate, is expelled from the surface of the substrate. For example, some coating materials may cost as much as $1500 to $5,000 a liter. With spin coating an amount of material is deposited which may include coating material sufficient to allow for 90% of the material to be thrown off in the spinning process.
It should be appreciated that the current state of the art, utilizing spin coating, does not adequately address the need for applying coatings of relatively viscous coating material. Because these materials are much more reluctant to migrate in response to the centrifugal forces, higher spinning speeds may be required, thus resulting in greater amounts of expelled material. Likewise, in order to provide a uniform coating, i.e., adequately disperse any center accumulation or pooling of the thicker material, longer spin times may be required, also causing additional waste.
Similarly, spin coating does not lend itself to providing thick coatings or coating surfaces with severe topography. The spinning necessary to cause migration of the deposited pool of coating material generally leaves a very thin layer of coating material remaining on the substrate. If thicker coatings are required a different process must be utilized, thus necessitating additional equipment if both thick and thin coatings are to be used at a single facility, or multiple thin coats must be applied, also introducing typically undesired characteristics such as additional processing time and a stratified end product. Moreover, many of the wafers or substrates have a fairly high degree of surface topography or surface roughness of various features for which spin coating is not particularly well suited to provide uniform coverage of those severe features.
Additionally, such spinning results in the coating of the periphery or circumferential edge of the wafer, in addition to typically causing an edge bead, or area of slightly thicker coating at the edge of the wafer, to form. These edge beads and edge coatings must typically be removed in a subsequent processing step as they may gum up the hot plates and downstream systems if the coating material, such as resist, is left on the edge or has crept around the back side of the substrate during the spin operation. Therefore, the current art of spin coating of a wafer requires additional steps in order to clean the expelled material from equipment as well as to remove the edge coating and edge bead formed. For example, current coating processes may employ another fluid dispense system that lends itself to removing this unwanted coating material from the substrate therefore introducing additional cost and/or more production facility floor space.
A further drawback of the state of the art spin coaters is that they are not adapted, or adaptable, to accommodate a variety of substrate sizes. For example, due to the precise spin speeds which must be maintained in order to produce a coating of a desired thickness, a spin chuck, and it attendant spinning mechanism, may not be acceptable for use in spinning particular size substrates. Accordingly, various sizes of substrates may require a variety of spin chucks and their associated component.
Moreover, the equipment utilized in spin coating the substrate must be adapted to handle particular sizes of substrates. For example, as spinning necessarily casts off coating material, the spin mechanism must typically include a spin bowl to catch this material. This spin bowl will define the largest substrate which may be accommodated by the mechanism. Likewise, in order to introduce the coating material at or near the center of the substrate, a delivery mechanism must be adapted to pump coating material from a reservoir to the center of the substrate surface which, as the substrate sizes to be handled increases, affects this delivery mechanism.
Other constraints on the ability to adapt to various size substrates include the actual chuck utilized to hold the substrate for coating and spinning. One chuck design generally used in spin coating is a vacuum chuck, wherein the surface of the chuck includes vacuum orifices in order to draw down a substrate placed thereon and firmly hold the substrate for spinning. Accordingly, a substrate which is smaller than this chuck will result in coating material which is expelled from the substrate surface onto the chuck surface requiring cleaning prior to engaging subsequent substrates. Additionally, the coating material may be introduced into the vacuum system which, at the least, may cause later problems in establishing a proper vacuum and, because of this material""s, and the solvents used in cleaning such materials, often volatile nature, may quite likely cause much more drastic results. Therefore, although a vacuum chuck having different vacuum positions that allow you to have the different form factors on it may not be practical for particular applications and/or for a particular range of substrate sizes.
Further, spin coating primarily lends itself to coating of circular objects, such as the typical silicon wafer. This limitation is due to balancing requirements of the substrate when spun at relatively high speeds as well as the windage problems resulting from spinning an irregular or other than circular shape.
Furthermore, as different size and/or dimension form factors of substrates are used, the coating apparatus must still achieve the same level of uniformity of the coating. Spin coating necessarily requires a longer time for coating of the outer edges of a large substrate than a small substrate. Accordingly, uniformness in coating the substrate may be difficult to attain. Irregular shapes, where it is not an equal distance from the center of the substrate to each outside edge, or all portions of the outside edge, compound this problem.
A still further drawback in the current state of the art is the time required to complete the coating of the substrate. Spin coating requires a particular amount of time, in addition to the time required to initially deposit the coating material upon the substrate, in order to cause the coating material to migrate fully across the surface. This time requirement is particularly prominent with more viscous coating materials because when spin coating a spinning action is used to spread the thick material from the center of the wafer out towards the outer edges and that process usually takes longer with the high viscosity fluids.
These and other objects, features and technical advantages are achieved by a system and method which utilizes extrusion of coating materials in applying a desired coating and is adaptable to accommodate various substrate types, form factors, and sizes ranging from squares to all different types of rectangles and circles. Preferably, the present invention utilizes a module that is easily adapted to different configurations.
The present invention utilizes an extrusion head in order to deposit coating material upon the surface of a substrate to be coated. Accordingly, precise thicknesses of coating material may be deposited without the waste associated with the aforementioned prior art spin coating method. For example, where 90% of the coating material initially deposited on a substrate is lost in spin coating, 95% or more of the coating material deposited by the preferred extrusion coating is utilized in coating square or rectangular substrates and approximately 79% of the coating material depicted by the preferred extrusion coating is utilized in coating circular substrates in one preferred embodiment of the present invention. The use of extrusion heads and chucks adapted for use in extrusion coating according to a preferred embodiment of the present invention are shown and described in the above referenced patent application entitled xe2x80x9cLinear Extrusion Coating System and Method.xe2x80x9d
Moreover, extrusion coating according to the present invention is well suited for the application of relatively thick coatings as well as the application of viscous coating materials. Likewise, because the use of an extrusion coating head allows the controlled depositing of the coating material throughout the surface of the substrate, shapes and form factors other than circular substrates may be handled with ease.
A preferred embodiment of the present invention includes a cantilevered extrusion head mounting assembly in order to allow for the accommodation of various sized and shaped substrates. This design enables the support of the head to be suspended out over the substrate, which through the use of a very strong and stable cantilever bearing assembly, provides for the accommodation of various sizes, lengths and shapes of extrusion heads.
Advantages are realized in the preferred cantilever design, providing movement of an extrusion head sufficient to coat substrates, over that of other designs, such as a bridge configuration with bearings disposed on either side of the substrate. Specifically, with a bridge type configuration, when trying to accommodate different size substrates to be coated it becomes necessary to change out the whole frame assembly in order to span a larger substrate and to support a wider extrusion head. However, by utilizing a cantilever design, it is not necessary to provide that additional outside support. Therefore, redesign in the frame and support area to accommodate substrate sizes which may change from time to time may be avoided. Moreover, the cantilever design provides a more accessible working area.
In being able to reach the full size of a substrate placed on a holding chuck, various distances of travel may be required for an extrusion head depositing the coating material. Thus the preferred cantilevered design provides for a sufficient length of extrusion head travel to apply a coating to such substrates. Accordingly, by either restricting the travel of the extrusion head and/or discontinuing the extrusion of coating material from the extrusion head, smaller substrates may be accommodated by this design.
Furthermore, accommodating a relatively wide product requires the supports for the extrusion head to be positioned so as not to interfere with substrates having such widths. The preferred cantilevered design requires only a single mounting point for the extrusion head movement assembly. Accordingly, any width of material may be placed beneath such an apparatus and be coated provided the extrusion head is sufficiently sized to coat the substrate.
A preferred embodiment of the present invention utilizes a universal mounting bracket on the cantilever mounting portion that allows the installation of substantially any head of any length or configuration in order to accommodate the particular product being run. Preferably, the head mounting assembly is adapted to interface with a plurality of substrate processing station modules in order to allow configuring of modules for particular applications or to provide particular desired attributes. Where the module configuration of the coating apparatus is a relatively narrow footprint, as is achievable by the aforementioned cantilever design, it lends itself to building clusters of them to provide stand alone modules tied together through robotics and/or being controlled by one central computer. Such an arrangement provides advantages in allowing for improved throughput of processed substrates. Moreover, such a modular design provides for easily adapting a particular substrate processing system to be adapted for a variety of differing processes by simply removing one variety of the coating module and replacing it with a different variety of the coating module, i.e., the modules may be designed to easily interface with other processing equipment in order to provide xe2x80x9cplug and playxe2x80x9d type interchange and/or upgrade.
Preferably, the coating modules of the present invention include a number of configurations each adapted to have particular attributes which may be desirable depending upon the particular end goal of the coating application. These configurations may include a walking shim module, wherein a coating shim is provided to prevent edge bead and edge coating problems while adapted to allow cleaning of the shim without adversely affecting throughput, a continuous shim module, wherein a coating shim is provided to prevent edge bead and edge coating problems while adapted so as to not require cleaning of the used shim, a spin clean chuck module, wherein a chuck is adapted to provide improved extrusion coating of the substrate which may be easily cleaned by spinning, a ring clean chuck module wherein a ring is adapted to provide improved extrusion coating of the substrate which may be easily cleaned, and a extrude and spin module, wherein a chuck is adapted to both hold the substrate for extrusion as well as further coating processing with spinning. Spinning of the substrate may be omitted in producing the designed uniform coating according to the present invention.
Each of the above modules of the present invention have certain common features. For example, in order to provide for interchangeability as described above, each of the module configurations is disposed within a same basic frame size and structure. In the preferred embodiment, each module is provided with a fixturing plate, such as an xe2x80x9cLxe2x80x9d shaped plate or rectangular base plate, that mounts the extrusion head movement mechanism, such as the aforementioned cantilever mounting mechanism, providing extrusion head access to the substrate. Preferably extrusion head movement is linear and provided by a granite air bearing with a linear motor although other means may be utilized for providing precise control of extrusion head movement including a conventional bearing or another type of drive system, such as a ball screw or a belt drive.
Additionally, each module preferably includes an extrusion head mounting mechanism which mounts extrusion heads of various sizes on the cantilever arm. Accordingly, not only may different modules be utilized to provide particular desired attributes in coating, but so too may each module be adapted for various sizes of substrates to be coated.
Preferably, the fixturing plate includes stations for necessary maintenance of the extrusion head. For example, located on one side of the base plate described above is preferably a storage and cleaning station for the head. Moreover, there may be multiple stations such as a head servicing station where the extrusion head can be disassembled or material can be flushed from the head located adjacent to the storage and cleaning station. The locating of such stations within the module, whether actually a part of the fixturing plate or disposed separately, provides for the head to be located automatically above these stations in addition to the actual coating operation onto the substrate.
The preferred embodiment fixturing plate is mounted within the standard size module and preferably is configured in such a way that the remaining portion of the module is not occupied by the fixturing plate, i.e., the module provides a very open format such that other types of sub-assemblies or sub-modules can be integrated into the overall main module. This allows the introduction of the above mentioned shims, spin chucks, or cleanable rings, which may be added depending on the particular customer""s requirements or the ultimate end use of the main module. Additionally, different size or different shape substrate can be accommodated by interchanging this sub-module which would preferably include the substrate mounting and the interface components to the robotic load, unload or automatic load, unload of the substrate.
In the preferred embodiment of the present invention the module includes the various componentry required to provide the desired coating of the substrate. This may include one or more solvent containers for supplying fluid up to the necessary components for head washing or maintenance, and may also include the main process fluid reservoir as well as the filtration and dispensing pumps that would be used to filter the process fluid and then ultimately dispense it up through the extrusion head onto the substrate. Accordingly, a preferred embodiment of the present invention includes, beneath the level of the L-shaped plate and the substrate fixturing sub-module, a lower cabinet where many of the solvents and process fluid that are required for the system are mounted. This cabinet may be exhausted to provide for the dissipation of harmful fumes. Of course, the disposition of the reservoirs, pumps, etcetera within a cabinet associated with the module of the present invention is optional. For example, where the module is to be associated with a larger system already providing the aforementioned componentry, the componentry may be remotely located, if desired.
Also, an electronics package will generally be required for the operation of the electrical and pneumatic components, the storage of process recipes, and the interface with the operator or with the host system in cases where this module is integrated into a main system. The electronics package may be located within this module, such as within the aforementioned cabinet. However, the electronics package, or a portion thereof, may be located elsewhere, such as above the module in an area where it may be more convenient to locate the electronics package or alternatively the electronics package may be in a remote location then connected by cables to the main coating module.
Preferably, the coating modules of the present invention are adapted to be integrated into certain systems, such as the TOK SS2 or TOK Sky Walk Automated Coating System available from TOK, Tokyo Ohka Kogyo of Tokyo, Japan. Additionally, or alternatively, the modules of the present invention are adapted to operate in stand alone mode. Likewise, the modules of the present invention are preferably adapted to be integrated into a cluster type or in line type of coating system. Accordingly, a single module may be utilized in a stand alone fashion until such time as processing demands require greater throughput and then the same module may be integrated with other processing equipment.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.